A-LevelChemistryAnalytical techniquesMay/June 2025Paper 3 Q115 Marks
Acids donate H⁺ in aqueous solution. The number of moles of H⁺ donated per mole of acid is the proticity of the acid. For example, sulfuric acid is diprotic as it donates two moles of H⁺ per mole of acid. In this experiment you will carry out a titration to determine the proticity of citric acid, C6H8O7. FB 1 is aqueous citric acid containing 7.50 g dm⁻³ C6H8O7. FB 2 is aqueous sodium hydroxide containing 4.50 g dm⁻³ NaOH. FB 3 is thymolphthalein indicator.
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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